The IBM PC AT computer architecture has become industry standard architecture for personal computers, and is typically built around a CPU such as an 80286, 80386, 80486, or 80586 (Pentium .RTM.) microprocessor all manufactured by Intel Corporation. The CPU is coupled to a host (local) bus, capable of performing memory accesses and data transfers at high rates of speed (i.e., on the order of 10-66 MHz). The host bus generally includes 16, 32, or 64 data lines, a plurality of address lines, and various control/status lines.
The typical IBM PC AT-compatible computer also includes a system bus, sometimes referred to as an I/O bus. Such a system bus is used to interface communications between a host CPU and a peripheral device, or communications between peripheral devices and host memory. The system bus is coupled to the host bus via certain interface circuitry. The system bus includes generally 8, 16, or 32 data lines, a plurality of address lines, as well as control/status lines. Commonly used system busses include the PCI bus and the ISA bus, both well known in the art.
Also in recent years, and particularly with the growing popularity of notebook and laptop computers, efforts have been made to reduce the size and improve the manufacturability of PC AT-compatible computers. Specifically, several manufacturers have developed "chipsets", which integrate a large amount of the system interface circuitry and other circuitry onto only a few chips. Examples of a chipset used in a notebook computer is Viper-N.TM. produced by OPTi, Inc. of Milpitas, Calif. The interface circuitry integrated into chip sets often includes interface circuitry between the host bus and the ISA bus and/or the PCI bus. In efforts to reduce system hardware, as many computer system functions as possible are sought to be incorporated into a chipset.
Generally chipsets are composed of multiple chips, where chipset functionality is partitioned among the chips. For instance, one chip might perform DMA control, where another chip might perform IDE control.
While chipsets are often used in laptop systems, the signals required to be provided by a chipset often vary from vendor to vendor. Thus, chipset manufacturers are often forced to either design a chipset specific to each vendor or to provide a chipset which provide signals that support all vendors, i.e., make a more generic chipset. Typically, in such "generic" chipsets, pins are provided for all signals anticipated to be required by all vendors. Thus, in actual implementation by respective vendors, some signals will not be used and pins will be wasted.
One of the general trends in the computer industry is to make laptops and other PC-type computers smaller and lighter. Thus, any way to scale down chipsets in size, including pin count, is desirable.